hi Kitty,
I think that the guides at the palace were 300 - 400 baht. If you get one of these make sure that there english is good. Also remember the dress rules for the temples and DON"T believe anyone who tells you it is closed even the guards.....just try and find another entrance. Last trip we went to Marble Palace, Grand Palace, Reclining Budda and Temple of Dawn by ourselves in one day. Easy to get around but keep a map with you. Try and get hold of one that has English and Thai translations in case you need to ask directions. The person we have booked is 500bt for the day. You pay her transport and entrance fees but this is cheap. And if you have someone like this they can take you to all the places and you won't get lost. We also intend to quiz her on info about where to go to shop etc.
Also don't forget if you are going to be using the BTS a lot get a 15 trip pass. It cost us 300-350bt and we went everywhere for the 2 weeks we were there and still had credit.
If you want the name of guide let me know and you can email her and see if she is available. She has studied either here or US and is studying something and this is how she pays for her education.

Karin